Russian airstrikes in Syrian has displaced more than 130,000 people and exacted heavy civilian casualties, a senior U.S. official reiterated Tuesday.

In addition to civilian deaths, the airstrikes have targeted medical facilities, schools and markets, said State Department spokesman Mark Toner.

"We're deeply, deeply concerned about these reports of high civilian casualties," he said, adding the civilian displacement figures are counted from October through the first half of November.

The "indiscriminate" strikes ''hamper the efforts to get that humanitarian assistance to where it is most needed," said Toner.

An Amnesty International report cited evidence of Russian use of cluster munitions and unguided bombs in populated residential areas. Russia rejects the claims as "clichés and fakes".

Russian strikes may have killed Zahran Alloush - a top Syrian rebel commander of Jaysh al-Islam - who led one of the most powerful groups against the forces of Syrian President Bashar al-Assad.

Syria's army claimed responsibility for the strike, however, opposition figures blame Russia.

Toner was careful not to place on any side the responsibility for Alloush's death, but said Secretary of State John Kerry discussed the attack with Russian Foreign Minister Sergei Lavrov on Monday.

Since Sept. 30, Russia -- an ally of the Assad regime -- has targeted civilian areas and humanitarian facilities in Syria, according to U.S. officials.

The Syrian Network for Human Rights said in a recent report that Russia killed 583 people, including 570 civilians in Syria, since it launched its air campaign in September to support the Assad regime.

While the Kremlin says its airstrikes in Syria are aimed primarily at Daesh militants, some NATO members say Russia is targeting moderate opposition groups opposed to Assad.